Plant polyketide synthases leading to stilbenoids have a domain catalyzing malonyl-CoA:CO2 exchange, malonyl-CoA decarboxylation, and covalent enzyme modification and a site for chain lengthening

Amorpha fruticosa - A Noxious Invasive Alien Plant in Europe or a Medicinal Plant against Metabolic Disease?

Amorpha fruticosa L. (Fabaceae) is a shrub native to North America which has been cultivated mainly for its ornamental features, honey plant value and protective properties against soil erosion. It is registered amongst the most noxious invasive species in Europe. However, a growing body of scientific literature also points to the therapeutic potential of its chemical constituents. Due to the fact that A. fruticosa is an aggressive invasive species, it can provide an abundant and cheap resource of plant chemical constituents which can be utilized for therapeutic purposes. Additionally, exploitation of the biomass for medicinal use might contribute to relieving the destructive impact of this species on natural habitats. The aim of this review is to provide a comprehensive summary and systematize the state-of-the-art in the knowledge of the phytochemical composition and the potential of A. fruticosa in disease treatment and prevention, with especial emphasis on diabetes and metabolic syndrome. Also reviewed are aspects related to potential toxicity of A. fruticosa which has not yet been systematically evaluated in human subjects.

Proteomic analysis reveals the spatial heterogeneity of immobilizedTaxus cuspidata cells in support matrices

A proteomic approach was used to study the responses of Taxus cuspidata cells to local microenvironments in different zones of immobilized support matrices. Analysis of protein spots by 2-DE revealed significant differences in the abundance of 31 spots, 28 spots, and 23 spots in outer, middle, and central zone cells between the immobilized and suspended cells. Six of these proteins, identified by MALDI-TOF-MS, were involved in the regulation of carbohydrate, nitrogen, and sulfur metabolisms. Immobilization triggered an increase in taxol production of the immobilized cells in the middle and central zones compared to that of the suspended cells. A negative relation between taxol production and the mitotic index was observed in the cells in the immobilization support matrix. Cells in the outer zone had high mitotic index and low taxol production, while cells in the middle and central zones showed low mitotic index and high taxol production. The abundance of S-adenosylmethionine synthetase, which was identified as one of the differentially expressed proteins, was positively correlated to the cell division activity in the immobilized cell cultures.

Molecular characterization of a heteromeric ATP-citrate lyase that generates cytosolic acetyl-coenzyme A in Arabidopsis

Acetyl-coenzyme A (CoA) is used in the cytosol of plant cells for the synthesis of a diverse set of phytochemicals including waxes, isoprenoids, stilbenes, and flavonoids. The source of cytosolic acetyl-CoA is unclear. We identified two Arabidopsis cDNAs that encode proteins similar to the amino and carboxy portions of human ATP-citrate lyase (ACL). Coexpression of these cDNAs in yeast (Saccharomyces cerevisiae) confers ACL activity, indicating that both the Arabidopsis genes are required for ACL activity. Arabidopsis ACL is a heteromeric enzyme composed of two distinct subunits, ACLA (45 kD) and ACLB (65 kD). The holoprotein has a molecular mass of 500 kD, which corresponds to a heterooctomer with an A(4)B(4) configuration. ACL activity and the ACLA and ACLB polypeptides are located in the cytosol, consistent with the lack of targeting peptides in the ACLA and ACLB sequences. In the Arabidopsis genome, three genes encode for the ACLA subunit (ACLA-1, At1g10670; ACLA-2, At1g60810; and ACLA-3, At1g09430), and two genes encode the ACLB subunit (ACLB-1, At3g06650 and ACLB-2, At5g49460). The ACLA and ACLB mRNAs accumulate in coordinated spatial and temporal patterns during plant development. This complex accumulation pattern is consistent with the predicted physiological needs for cytosolic acetyl-CoA, and is closely coordinated with the accumulation pattern of cytosolic acetyl-CoA carboxylase, an enzyme using cytosolic acetyl-CoA as a substrate. Taken together, these results indicate that ACL, encoded by the ACLA and ACLB genes of Arabidopsis, generates cytosolic acetyl-CoA. The heteromeric organization of this enzyme is common to green plants (including Chlorophyceae, Marchantimorpha, Bryopsida, Pinaceae, monocotyledons, and eudicots), species of fungi, Glaucophytes, Chlamydomonas, and prokaryotes. In contrast, all known animal ACL enzymes have a homomeric structure, indicating that a evolutionary fusion of the ACLA and ACLB genes probably occurred early in the evolutionary history of this kingdom.

Novel polyketides synthesized with a higher plant stilbene synthase

The physiological function of the stilbene synthase (STS) from groundnut (Arachis hypogaea) is the formation of resveratrol. The enzyme uses 4-coumaroyl-CoA, performs three condensations with malonyl-CoA, and folds the resulting tetraketide into a new aromatic ring system. We investigated the capacity for building novel and unusual polyketides from alternative substrates. Three types of products were obtained: (a) complete reaction (stilbene-type), (b) three condensations without formation of an aromatic ring (CTAL-type pyrone derailment), and (c) two condensations (BNY-type pyrone derailment). All product types were obtained from 4-fluorocinnamoyl-CoA and analogs in which the coumaroyl moiety was replaced by furan or thiophene. Only type (b) and (c) products were synthesized from other 4-substituted 4-coumaroyl-CoA analogs (-Cl, -Br, -OCH3). Benzoyl-CoA, phenylacetyl-CoA, and medium chain aliphatic CoA esters were poor substrates, and the majority of the products were of type (c). The results show that minor modifications can be used to direct the enzyme reaction to form a variety of different and new products. Manipulation of the biosynthesis of polyketides by synthetic analogs could lead to the development of a chemical library of pharmaceutically interesting novel polyketides.

Evidence for catalytic cysteine-histidine dyad in chalcone synthase

Chalcone and stilbene synthases (CHS and STS) catalyze condensation reactions of p-coumaroyl-CoA and three C(2)-units from malonyl-CoA, but catalyze different cyclization reactions to produce naringenin chalcone and resveratrol, respectively. Condensing activities of wild-type CHS and STS as well as STS-C60S mutant were inhibited by iodoacetamide (Idm) and diethyl pyrophosphate (DPC). DPC also inhibited malonyl-CoA decarboxylation activity of wild-type and C164S mutants of CHS and STS. Meanwhile, Idm treatment enhanced (two- to fourfold) malonyl decarboxylase activity of wild-type enzymes and STS-C60S, whereas this priming effect was not observed with C164S mutants of CHS and STS, indicating that the cysteine residue being modified by Idm is the catalytic Cys164 of CHS and STS. DPC inhibition of decarboxylation activity of wild-type CHS was pH-independent in the range of pH 5.8 to 7.8; however, its inhibitory effect on CHS-C164S increased as pH increased from 6.2 to 7.4 with a midpoint of 6.4. Based on the 3-D structure of CHS and the observed shift in microscopic pK(a), it was concluded that the histidine residue being modified by DPC in CHS is likely the catalytic His303 and that His303 forms an ionic pair (catalytic dyad) with Cys164 in wild-type CHS. In addition, our results showed that Cys60 in STS is not essential for the activity and only a single cysteine (Cys164) participates in the catalysis as in CHS.